1. Field of the Invention
The present invention relates to laser generators and a method of producing modulating data therefor used in laser printers, etc., and more particularly to such generator which provides invariably stabilized exposure light for a photosensitive drum using a simple structure and a method of producing modulating data therefor.
2. Description of the Prior Art
At present, laser printers are applied in various picture information output devices such as digital copying machines and facsimile output devices. FIG. 1 schematically illustrates the relationship between a laser scanner constituting an exposure device and a photosensitive body on which a static latent image is formed by such exposure in a laser printer.
In FIG. 1, reference numerals 10 and 20 denote a laser scanner and a photosensitive body (or drum), respectively. In the laser scanner 10, reference numeral 11 denotes a laser beam emitting element such as a laser diode which emits a laser beam LB, which is reflected by a polygon mirror 12 and then a reflective mirror 13, which constitute part of the laser scanner 10, and irradiated onto the photosensitive drum 20. The polygon mirror 12 is driven by a polygon motor (not shown) to rotate in the direction of the arrow A. The direction of reflection of the laser beam LB by the polygon mirror 12 is sequentially altered in accordance with the rotation of the polygon mirror 12 and the laser beam LB irradiated onto the drum 20 is moved along the axis of the photosensitive drum 20 (as shown by the arrow B in FIG. 1). in this way, the laser beam LB scans the surface of the photosensitive drum 20. Further, if the drum 20 is rotated in the direction of the arrow C and the laser beam LB modulated in accordance with image data is generated by the laser beam emitting element 11, a static latent image corresponding to the image information is formed on the photosensitive surface of the drum 20.
Usually, a photosensor 14 is provided in the vicinity of one end of the photosensitive drum 20 in order to obtain line synchronization in the exposing procedure. In such apparatus, the laser beam emitting element 11 is forced to emit a laser beam at the start of exposure and at the end of exposure for one line. When the photosensor 14 senses this emitted laser beam LB, exposure for a respective one of successive lines is performed using a signal indicative of the detection of the laser beam LB as a horizontal synchronizing signal.
With such conventional laser printer (especially its laser scanner 10), laser modulations are controlled by using image data (serial data corresponding directly to image information) in such a uniform manner that, for example, the laser beam LB is subjected to on control (actually the laser beam LB is emitted and irradiated) when the image data is in the on interval during which the logical level is "1" while the laser beam LB is subjected to off control (the emission of the laser beam LB is stopped or interrupted) when the image data is in the off interval during which the logical level is "0". Therefore, even if, for example, the surface potential (mainly the exposure potential) of the photosensitive drum 20 fluctuates and hence the laser exposure width changes due to changes in the temperature within and aging of the printer, etc., it is usually impossible to compensate for these fluctuations and changes.